Furnace control apparatus



J. A. ASHWORTH FURNACE CONTROL APPARATUS July 27, 1943.

Filed Feb. 27, 1941 TEMPERATURE m RECORDER /2- /'/l H/GH RES/STANCE FURNA as a RELAY 2 /s NMNWWNH R 12 53 l MMMMQM17 El k f 3 x 2a 27 C FIG. 3

INVENTOR JA-ASHWORTH @MEWM A T TORNEY Patented July 27, 1943 FURNACE CONTROL APPARATUS Joseph A. Ashworth, North Arlington, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February z7;1941, Serial No. 380,761 3 Claims. (01. 236-46) This invention relates to a-method of and apparatus forcontrolling the heating and coolingrates of a furnace.

The object of the invention is to provide a simple method of and very effective means for ac-' curately controlling the heating and cooling rate of a furnace.

In accordance with this invention there is added to the'electromotive force of a thermocouple located in the furnace another electromotive force. The application of the second electro motive force is controlled with time and the output of thethermocouple with the sec nd electromotive force added thereto is use "in controlling the application of heating energyto the furnace.

In the drawing:

Fig. 1 is a schematic diagram of the system and apparatus employed in practicing the'invention; and

Figs. 2 and 3, drawn on enlarged scales relative ,to Fig. 1, show details of parts shown in Fig. 1.

The furnace l shown in Fig. 1 is heated by means of a coil 2 supplied with current from a suitable source of current supply 3 through condoctors 4, 5, an obvious circuit 6 and a transformer I.

A thermocouple 8 extends into the furnace i to detect changes in the temperature of the furnace, the thermocouple 8 being connected by means of conductors 9, H], H and I2 to a temperature recorder 13 which may be of conventional type. The .thermocouple 8- is also electrically connected to alocal circuit i4 containing a high resistance relay 15, a source of current supply l6, rheostat I! and a potentiometer l8. The source of current supply I6 supplies to the high resistance relay IS an electromotive force in addition'tothe electromotive forcedeveloped in the thermocouple 8. The circuit for energization of the relay i may be traced as follows: local battery I8, conductor l9, conduc-' tor 20, winding of relay I5, conductor 2i, conductor 9, thermocouple 8, conductor i0, conduc atingcurrent from the source 3 over the con ductors 4, 5, 21 and28 and through cam controlled contacts of a switch 29. The motor 26 drives a shaft 30 to rotate the cam 3| of the switch 29 and the rotatable coil 32 of the potentiometer Hi. The cam 3i of the switch 29 is so I supported on the shaft 30 that it may be rotated I on the shaft 30 or made to rotate with the shaft and is provided with a projection 33 to operate contacts 34.and 35 'of the switch 29.

Fig. 2 shows a convenient way of mounting the cam 3| on the shaft 30. In this case the shaft 30 is enlarged to provide a flange 36, a cylindrical portion'3'i and a male threaded portion 38. The cam 3i is journaled on the portion 31 and is held in required position by means of washers 39 and 40 and a nut 41. The washer 39 vary with time the electromotive force added to chronous motor 26 which is supplied with oper- 55 is interposed between one face of the cam 3i- .be of any desired form found suitable for the purpose. In this case the potentiometer I8 is shown in the form of a double slide wire potentiometer comprising as shown in Fig. 3 an insulating disc 43, the resistance coils 44 and 45 and a U-shaped wiper contact 42. The disc 43 supports the coils 44 and 45 and is removably mounted on the shaft 30. naled on the shaft 30 but is normally held against rotation relative to the shaft 30 by means of friction washers 46 and 41 and a nut 48 which is mounted on a' male threaded end 49 of the shaft 30. Thewasher 4B is interposed between one face of the disc 43 and a flange 50 on the shaft 30, the washer 41 being interposed between the otherface of the disc 43 and the nut 48. The wiper contact 42 is supported on a fixed support 5| and bridges the resistance coils 44 and 45.

It will be seen by looking at Fig. 1 that when the resistance coils 44 and 45 are rotated in a" clockwise direction and relative to the f xed wiper contact 42 the resistance across the lower branch of the circuit I4 is increased resulting inv the application of more. of the current from the battery I 6 to the high resistance relay l5.- When the combined electromotive force of the thermo-' couple 8 and that supplied from the battery l6 reaches a certain value the high resistance relay The disc 43 is jour- 95 is energized to pull its armature 52 away from back contact 53 to open the circuit 54, included in-which is the relay 55 controlling the circuit through which current is supplied to the transformer l. Deenergization of relay 55 releases its armature 56 from front contact 51 and opens the circuit 6 to shut oil the current supply to the heating coil 2. The circuit 54 may be traced as follows: source of current supply 3, conductor 5, conductor 58, armature 52 and back contact 53 of relay l5, conductor 59, lower contacts 35 of switch 29, conductor 6G, winding of relay 55, conductor Bl, conductor t-to current supply 3.

When the motor 26 is operated to rotate the shaft 30 to cause rotation of the disc Q3 of the potentiometer IE it also causes rotation of the cam 3i of the switch 29. The motor continues to operate until the projection 33 moves an arm 62 controlling the switch contacts 31% and '35. Downward movement of the arm 62 will cause opening of the contacts 3 3 and 35; Since the motor 26 is supplied with current through the contacts 34, opening of these contacts will cause the motor 26 to stop. Opening of the contacts 35 will cause deenergization of relay 55 to allow its armature 56 to fall away from front contact 57 so that circuit 6 will be opened and the heating coil 2 will be deenergized at the end of the heat treatment even though relay 15 might not at that time be energized to open the circuit 54?. The cam 3| is shown in Fig, 1 with the projec tion 33 rather close to the arm 62 of the switch 29. Under this condition the furnace i would be operated for a relatively short heat treatment of a piece of work in the furnace. The length of the heat treatment may be changed, however, by changing the position of the projection 33 relative to the arm 62. This can be accomplished by loosening the nut ll and then rotating the cam 3i onthe shaft 30 to bring the projection 33 to a required position and then tightening the nut M The electromotive force to be added to the electromotive force of the thermocouple 8 may be set to some required value by a suitable set ting of the rheostat H and is thereafter varied by operation of thepotentiorneter 58. In Fig. 1 the electromotive force added to that of the thermocouple 8 is gradually increased since the resistance coils M and $5 are rotated in a clockwise direction relative to the fixed wiper contact 432 thus putting more resistance in the shunt across the lower branch of the circuit M and as a consequence making more of the electromotive force supplied from the battery It to be applied to the relay I5. When the electromotive force from the thermocouple 8 plus that from the bat tery I6 reaches an operating value for the relay I5 the relay operates to open the circuit 56. Opening of the circuit 5% causes deenergization of relay 55 to cut off" the supply of heating current to the coil 2... With its heating current supply cut off, the temperature of furnace l and also the electromotive force of the thermocouple 8 decreases. When the combined electromotive forces of thermocouple 8 and that across potentiometer l8 fall below the operate value for relay I5, this relay releases to close circuit 5% which -reapplies heating current to the furnace.

increasing the electromotive force supplied to the relay 15 from the battery It with time in the manner above described the amount of heating current to the furnace may be so varied that the cooling rate of the furnace may be controlled to give a desired heat treatment.

If it is desired to control the heating rate of the furnace I so that the furnace will be brought to a required high temperature at a slower rate' than its normal heating rate and at the end of a certain period of time, the disc 83 may be removed from the shaft 30 and then placed back thereon but in a reverse position. In this case clockwise rotation of the disc 63 will cause a gradual lessening of the resistance across the lower branch of the circuit I l and lessening of the potential supplied to the relay l5 from the battery l6.

By virtue of the method and apparatus deupon an electrical device which is also influenced and acted upon by the electromotive force developed in the furnace thermocouple. Since the electrical device acted upon by the combined electromotive forces coming from the furnace thermocouple and the external source of supply is arranged-to control the application of heating energyto the furnace the temperature of the furnace may be controlled by merely varying the control voltage in accordance with a predetermined program.

What is claimed is:

1. An apparatus for controlling the temperature of a furnace in accordance with desired programs, comprising in combination, a heating device in the furnace, a circuit including a source of current supply for said heating device, a relay having contacts in said circuit and operable to control the opening and closing of said circuit, a control circuit for said relay, a thermocouple in said furnace, a local circuit including a local source of current supply, a rheostat and a high resistance relay in said local circuit and connected in series with said thermocouple, a potentiometer connected across said local circuit in shunt of said local source of current supply and said rheostat, said high resistance relay being operable by electromotive forces supplied by said thermocouple and said local source of current I supply, and said potentiometer being operable to by means of said high resistance relay, a motor,v

a shaft driven by means of said motor and operable to control the operation of said potentiometer, a switch in said control circuit, a cutout for said motor and means mounted on said shaft and operable to open said switch and the cut-out for said motor at the end of the desired program.

2. An apparatus for controlling the temperature of a furnace in accordance with desired programs, comprising in combination, a heating device in the furnace, a circuit including a source of current supply for said heating device, a relay having contacts in said circuit operable to control the opening and closing of said circuit, a contr01 circuit for said relay, a thermocouple in said furnace, a local circuit including a local source of current supply, a rheostatand a high resistance relay in said local circuit and connected in series with said thermocouple, a potentiometer connected across said local circuit in shunt of said local source of current supply and said rheostat, said high resistance relay being operable by electromotive forces supplied by said thermocouple and said local source of current supply, said potentiometer being operable to con- -trol the electromotiye force supplied from said local source oi current supply to said high resistance relay by increasing or decreasing the resistance shunting said local source of current supply, contacts in said control circuit and operated by means of said high resistance relay, said high resistance relay operating to open its contacts in said control circuit when the electromotive force produced in said local circuit is a required yalue, a motor connected to said source of current supply, a cut-out switch for said motor,

- a switch in said control circuit, a rotatable shaft connected to said motor and said potentiometer and serving as means to operate said poten-,

tiometer, a cam supported on said shaft and operable to open said switches at the end of the program and said cam and potentiometer being so supported on said shaft that they may be adjusted to positions for required programs.

3. An apparatus for controlling the temperature of-a furnace in accordance with desired programs, comprising in combination. a heatingdevice in said furnace, a circuit including a source of current supply for said heating device, a relay having contacts in said circuit operable to open and close said circuit, a control circuit forsaid relay, a thermocouple in said furnace, a local circuit including a local source of current supply, a rheostat and a high resistance relay in said local circuit and connected in series with said thermocouple, a potentiometer connected across said local circuit in shunt of said rheostat and in shunt of said local source of current supply, said high resistance relay being operable by electromotive forces supplied by said thermocouple and by said local source of current supply,

Y said potentiometer being operable to control the value, a motor, a current-supply circuit for said motor, a cut-out switch in said current-supply I circuit, a cut-out switch in said control circuit, a rotatable shaft driven by means of said motor and operating said potentiometer, a cam adjustably supported on said shaft and operable to open said cut-out switches at the' end of the program and means mounted on said shaft and adjustably holding-said cam and said potentiometer in such positions that the apparatus will operate for a predetermined program.

' JOSEPH A. ASHWORTH. 

